CVE-2026-62676: Omnigent Guardrail policy bypass: shell-command parser fails open in policies/builtins/_shell.py

The shared shell-command parser fails open. When a gated command spells something the parser doesn’t recognize, it produces no operation, the policy evaluator returns None, and None = abstain = ALLOW. So any command the parser misses bypasses both the GitHub repo/branch allowlist and the working-directory confinement — the product’s two core safety guarantees.